Classify on test data, number of instances shows of training data

Question

I have a dataset and I divided the dataset into training set(70%) and test set(30%). The total number of instances in my dataset is 1816. Training set has 1273 instances and test set has 543 instances. I used Naive Bayes classifier for classification purpose. I am using Weka software for classification. When I provide test dataset using classify tab in Weka, I found after classification it shows number of instances 1273. I provided test set where number of instances 543. However if I take a look on the confusion matrix

   a   b   <-- classified as
  31  44 |   a = Yes
  36 432 |   b = No

As you can understand from confusion matrix if I add 31+44+36+432 = 543

I can not understand why I saw the number of instances of training set (1237) while I am doing classification on test set.

I opened the training set using open file button on preprocess tab and then go to classify tab and supplied test set.